I want to be able of partial tracing the `X`

variable defined below :

```
using ProxSDP, JuMP
model = Model(with_optimizer(ProxSDP.Optimizer, log_verbose=false))
@variable(model, X[1:N,1:N], PSD)
```

where `N>=1`

. I tried using `QuantumInformation.ptrace`

but it didn’t work.